Method for the purification of carbohydrates obtained by hydrolysis of cellulose by means of hydrochloric acid



Patented Aug. 11,- 1931 UNITED STATES PATENT OFFICE ERIK HAGGLUND, OFABO, FINLAND, ASSIGNOR TO THE FIRM HOLZHYDROLYSE AKTIENGESELLSCHAFT, OFHEIDELBERG, GERMANY METHOD FOR THE PURIFICATION OF CARBOHYDRATES OEB'IAINED BY HYDROLYSIS OF CELLULOSE BY MEANS OF HYDROGHLOBIG ACID 7 NoDrawing. Application filed December 10, 1928, Serial No. 825,129., andin Germany December 14, 1927.

It is known that by hydrolysis of cellulose containing material such aswood, preferably in the form of saw dust, by means of hydrochloric acida carbohydrate product can be obtained. However this carbohydrateproduct or sugar is, even after having been subjected to an evaporationprocess with a view to removing the hydrochloric acid therefrom, notvery well adapted for 10 use as food material owing to certain residuesof acid in it which cannot be removed by evaporation, and whichdeteriorate the taste of the product and its salubrity. Attempts havealready been made to overcome this difiiculty by subjecting the productof the hydrolysis to a purifying process consisting in transforming thecarbohydrate into saccharate and subjecting the saccharate to a washingprocess and thereafter recoveringthe sugar by decomposition of thesaccharateby carbonation. However the effect of this purification is notentirely satisfactory. Moreover a considerable loss in saccharate iscaused by the washing process. Now this invention has for its object toavoid thedeficiency of the above mentioned known purification process bythe application of a special method for the transformation of thecarbohydrate into saccharate.

' This special method according to the invention consists in that thecarbohydrate or sugar suitably after a preliminary partial removal ofacid by evaporation is subjected to wet grinding together with an addedoxide or hydroxide of an alkaline earth-metal preferably slaked lime.The, grinding is advantageously effected in a so-called ball-mill, thegrinding bodies of which consist of porcelain.

The effect of the grinding process consists in that the'carbohydrate isvery completely converted into saccharate and that the acidresidueremaining, as above mentioned, in the carbohydrate even afterevaporation is bound to the alkaline earth metal. The ground material isthereafter subjected'to a draining operation, preferably by subjectingit to centrifugation in a centrifuge having a bowl with pervious wall.If so treated, together with the liquid, also a considerable part of thechlorides dissolved therein are removed. Inorder to remove also the lasttraces of chlorides it is advisable to subject the material, which hasbeen freed from liquid by centrifugation, to a washing process which maybe effected in.

the same centrifuge. This washing process requires only small quantitiesof water and does not cause a remarkable loss in saccharate. 1

In this way a saccharate is obtained which 7 is free from chlorides andwhich in known manner by saturation, that is treatment with carbonicacid, preferably under pressure can be converted into pure carbohydrate.

The liquid which is separated off by the centrifugation process containsbesides chlorides and other soluble substances also sugar material whichdoes not form insoluble saccharates. I

The product which. is obtained after saturation is a pure tastelesscarbohydrate, that is a carbohydrate which is neither sweet nor has anyother characteristic taste. It is possible to convert it into a sweetsugar by a so-called inversion process, for instance by heating it inthe presence ofsulfuric acid.

Example 100 parts by weight of a carbohydrate or sugar material,obtained by hydrolyz'ing saw dust with hydrochloric acid andconcentration of the product of hydrolysis by evaporation, are dissolvedby 400 parts by weight of water and the solution introduced into aball-mill with porcelain balls. 100 parts by weight of fresh slaked limeare added and stirred into the solution. The mixture is subjected to agrinding operation for a period of 1 hours. The ground product consistsof a thin impalpable pulp which is introduced ,into a centrifuge withpervious wall and subjected to centrifugation so as to remove the watercontained therein. The 'solid constituents of the pulp form] a denselayer adhering to the wall of the bowl. As soon as the water of thepulphas been removed ice-water is added, and

from the precipitated gypsum.

centrifu ation continued till no chlorine can be foun in the washingwater. The saccharate is retransformed into a pulp, this beingadvantageously done by re eated grinding with addition of water. guchsaccharate pulp is introduced into pressure proof receptacles andsubjected to saturation by treating it with carbonic acid at elevatedpressure, for instance at a pressure of two atmospheres. Thecarbohydrate is separated from the saturation sludge and in usual mannerconverted into invert sugar by heating with 2% sulfuric acid. The invertsugar solution is freed from sulfuric acid asusual by addition of chalkand se aration e solution is treated with active carbon and thereafterconcentrated by evaporation. The yield in pure sugar is about 65% byweight of the raw carbohydrate material or, if the raw carbohydrate hadbeen obtained by hydrolysis of saw dust, about 45% by weight of thehydrolyzed wood..

Considering the fact that about by weight of the wood can .be recoveredas carbohydrate by hydrolysis a portion of raw carbohydrate equal toabout 25% by weight of the wood remains in the solution separated oif bycentrifugation from the product of grinding the mixture of rawcarbohydrate and slaked lime. If desired, this solution can be subjectedto fermentation or be used in the manufacture of yeast.

The essentially novel steps of my. above described method are recited inthe annexed claims in connection with which it is to be understood thatthe term oxide of an alkaline earth-metal is intended to cover not onlythe oxide but also the hydroxide.

What I claim is A method of treating carbohydrates which have beenobtained by hydrolysis of cellulose with the aid of hydrochlorlc acidwhich comprises subjecting the carbohydrates in solution in admixturewith an oxide of an alkaline earth metal to grinding, removing chloridecontaining liquid from the solid material, washing the separated solidmaterial with fresh water, subjectin the washed solid material toreaction wit carbonic acid under elevated pressure so as to decomposethe saccharate and to liberate the carbohydrates, separating the sludgefrom the carbohydrate solution, and inverting the carbohydrate containedin the separated solution.

In testimony whereof I afiix my signature.

ERIK HKGGLUND.

